The present invention relates to valves appropriate for maintaining a vacuum. More particularly the present invention relates to a valve capable of isolating particle accelerator system components from exposure to atmosphere while maintaining a vacuum in other system components when the valve is closed, and capable of permitting particle beam passage through the valve when open.
Particle accelerator systems are currently available in a variety of types, configurations, and sizes. One consistent feature among these systems, however, is that the interior volume of the particle accelerator system, in which the particle beam is generated and energized, is maintained in a state of vacuum during operation, typically through the use of vacuum pumps. (For the purposes of this specification, a xe2x80x9cvacuumxe2x80x9d should be understood to refer equally to a xe2x80x9cpartial vacuumxe2x80x9d.) Frequently, particle accelerator systems comprise a number of distinct components which are linked along the line of the generated particle beam. As with the particle accelerator system as a whole, the interior volumes of these components are also maintained in a state of vacuum during operation, though atmospheric pressures may vary from component to component.
The interior of these particle beam accelerator components must be accessed from time to time for maintenance, repair, and other purposes. This access may necessitate exposure of the components"" interior spaces to the atmosphere and thereby result in a loss of vacuum. However, this loss of vacuum can be advantageously limited to the individual components being accessed, if the accessed components are first isolated from the remainder of the particle accelerator system. Vacuum valves have previously been utilized within particle accelerators as a means of isolating certain beam line components from other components prior to exposure to atmosphere for maintenance, repair, or other purposes.
Traditionally, particle accelerator systems utilized commercially available valves, together with conventional vacuum flanges, to provide vacuum isolation where required. Valves of this type are relatively large (or xe2x80x9cthickxe2x80x9d) when measured parallel to the particle beam line, and the use of such relatively large valves in particle accelerator systems can result in a number of negative consequences.
To understand one way in which an overly xe2x80x9cthickxe2x80x9d vacuum valve can interfere with the performance of a particle accelerator system, one characteristic of the nature of particle beams should be understood. For the purpose of example only, consider a beam of positively charged Hydrogen ions. Due to the positive charge shared by the ions within the particle beam, the ions naturally repel one another, and the beam diameter therefore tends to expand over time and along the length of the particle accelerator system. Particle accelerators are therefore usually equipped with a series of focusing mechanisms (e.g. quadrupole magnets) to counter this quality of the particle beam.
In a particle accelerator system including multiple components, the diameters of the communicating apertures of adjacent components, through which the particle beam passes, may be limited in size to reduce interference between the operations of those adjacent components. The aperture of any vacuum valve through which the particle beam passes may be similarly limited. Particle beams are often focused to pass through such inter-component apertures with minimum interference from the aperture walls and edges. As the particle beam diameter will tend to expand along the entire length of the aperture between the internal spaces of two adjacent components (xe2x80x9cthe aperture lengthxe2x80x9d), it is desirable to limit the length of the aperture to prevent interference of the valve aperture with the particle beam. In summary, generally, the thicker the vacuum valve, the greater the aperture length, and the greater the likelihood of particle beam interference.
Accommodating thick vacuum valves is especially difficult toward the xe2x80x9clow energyxe2x80x9d end of particle accelerator systems where congestion among system components is most acutely experienced. In any location along the particle accelerator system a xe2x80x9cthickxe2x80x9d vacuum valve could infringe upon the space available for other devices along the beam line, reduce system efficiency, and increase system costs. For example, xe2x80x9cthickxe2x80x9d vacuum valves may necessitate the use of additional focusing mechanisms, thus further reducing beam line space and increasing costs.
Previously, Donald A. Swenson of Linac Systems constructed an xe2x80x9cUltra Thin Beamline Vacuum Valvexe2x80x9d which attempted to satisfy the problems associated with overly thick vacuum valves in particle accelerator systems. Specifically, Mr. Swenson developed a disk-shaped valve which measured only 0.25 inches thick in the direction of the beam line. The vacuum valve featured a relatively small valve aperture at the center of the disk, surrounded by bolts toward the edge of the disk for fastening the vacuum valve to, and sealing the valve against, neighboring system components. The Swenson valve featured a frame and a slide, the slide having a valve aperture on a canted sealing surface. The slide of the Swenson valve moved between a second closed position, in which the slide engaged the canted sealing surface to seal the valve aperture with the aid of an elastomer seal, and a first open position, in which the slide was moved away from the canted sealing surface and permitted the passage of a particle beam through the valve aperture. The sealing surface of the vacuum valve was canted for the purpose of reducing the wear on the elastomer seal located thereon during the opening and closing of the vacuum valve. The vacuum valve offered the advantages of relatively simple construction, featuring only a single moving part and being relatively inexpensive to manufacture. The valve could be constructed from aluminum or steel.
However, the design of the Swenson vacuum valve has serious limitations. One limitation of the Swenson vacuum valve is that the valve was not designed for construction from, or plating with, high purity copper. The interior surfaces of particle accelerator systems, and particularly of high energy particle accelerator systems, are preferably of high purity copper or some other highly electrically conductive material. Another limitation of the Swenson vacuum valve is that the valve, while substantially flat and smooth on one side, possesses significant irregularities on the opposite side. Specifically, the moving parts of the Swenson valve do not smoothly integrate with the surface of the valve""s non-moving frame. Such surface irregularities within the interior chambers of particle accelerator components, in which powerful electromagnetic fields are generated, creates a risk of detrimental electrical arcing.
Therefore a need exists for a thin beam-line vacuum valve which is both appropriate for use in the congested areas of a particle accelerator system, and which presents a smooth and highly electrically conductive surface toward both adjacent particle accelerator components.
The thin vacuum valve for particle accelerator beam lines of the instant invention addresses these needs. Specifically, the vacuum valve is easily constructed from highly electrically conductive material, such as oxygen-free high-purity copper, and presents smooth, flat surfaces toward each adjacent particle accelerator component. The valve is comprised of a frame, a slide, a shaft, and preferably a first and second clamp.
The frame has a slide axis, first and second surfaces respectively facing toward the two adjacent particle accelerator system components, and an outer frame wall between the first and second surfaces. The first surface of the frame includes a slide slot having a slot surface and a frame orifice extending through the frame between the first or slot surface and the second surface. The frame orifice is positioned and sized on the frame to permit passage of a particle beam generated by the particle accelerator system along a beam line;
The slide has a slide orifice, an outer surface, and an inner sealing surface. The slide is housed substantially within the slide slot and is movable between a first position and a second position along a slide axis. In the first position, the slide permits a particle beam to pass through the slide orifice and through the frame orifice along the beam line. In the second position, the slide prevents a particle beam from passing through the frame via the frame aperture. The inner sealing surface of the slide engages the slot surface of the frame when the slide is in the second position, thereby substantially vacuum sealing the frame orifice.
The shaft is translatable relative to the frame in a direction substantially parallel to the slide axis. The shaft extends from the slide in a direction substantially perpendicular to the slide axis and toward the outer frame wall. Translation of the shaft selectively controls the movement of the slide between the first and second positions.
The first clamp has a first inner clamp surface and an outer first clamp surface. The first inner clamp surface engages a first side of the slide and maintains the slide substantially within the slide slot.
The second clamp has a second inner clamp surface and an outer second clamp surface. The second inner clamp surface engages a second side of the slide substantially opposite the side of the slide contacted by the first inner clamp surface, and maintains the slide substantially within the slide slot.
The outer surface of the slide and the first surface of the frame form a substantially flat surface substantially perpendicular to the beam line and surrounding the slide orifice. The second surface of the frame forms a substantially flat surface substantially perpendicular to the beam line and surrounding the frame orifice.
In one embodiment, the slide has a first slide detent extending toward the first clamp and a second slide detent extending toward the second clamp, the first clamp has a first clamp detent extending toward the slide, and the second clamp has a second clamp detent extending toward the slide. The first clamp detent is positioned to engage the first slide detent, and the second clamp detent is positioned to engage the second slide detent, when the slide is moved from the first position to the second position. The inner surface of the slide is thereby biased toward the frame orifice and against the slot surface to substantially seal the frame orifice when the slide is in the second position.
In another embodiment, the frame of the valve is the end plate of one of the particle accelerator components.